Candela Laser Corporation proposes to develop a cw holmium laser stereotactic endoscopic neurosurgical treatment of hydrocephalus. Hydrocephalus is currently managed by the use of valved shunts to drain cerebrospinal fluid from obstructed ventricles. At present, shunt revision is by far the most common neurosurgical reoperation being performe Radiation from a 2.l micromole cw holmium laser is fiberoptically compatible, and has been shown in preliminary experiments to ablate soft tissue, leaving an approximately 500 micromole zone of thermal damage. Using the holmium laser under stereotactic endoscopic control, it should be possible to perform precise fenestration of ventricular walls. Ventricular fenestration is expected to eliminate the need for an implanted shunt and reduce morbidity and mortality in patients with hydrocephalus. The goal of the proposed work is to demonstrate that stereotactic endoscopic ventricular fenestration can be safely performed using a cw holmium laser, and that the procedure will provide a lasting and effective means of managing hydrocephalus caused by ventricular obstructions. In Phase I, the laser-tissue interaction will be studied in detail in animal experiments, and the surgical approach will be tested in human cadaveric studies. Phase II will begin with an evaluation of the procedure in an in vivo porcine model, followed by clinical trials.